Poor dental hygiene. The most common cause of bad breath is when the bacteria in your mouth break down the food caught in and around teeth. Infrequent brushing and flossing will let food particles cling to your teeth longer.
Certain foods — such as garlic, onions and some spices — can contribute to bad breath for up to 72 hours after eating. After digestion, the proteins in these foods circulate in the bloodstream. They are carried into the lungs and are expelled in your breath until they exit your system.
Cigarettes, cigars and chewing tobacco can cause dry mouth and bad breath, on top of being harmful to your overall health. Ask your dentist for help with quitting.
Bad breath can also be an early symptom of periodontal or gum disease. Gum disease is an infection that affects the gums and jawbone, which can lead to a loss of gum and teeth. If left alone, the bacteria will build up on your teeth and irritate the gums.
Dry mouth. Saliva helps cleanse your mouth and remove food particles. When you can’t produce enough saliva, bad breath can occur. Some medications, alcohol and breathing with your mouth open can all contribute to dry mouth.
Medical Conditions. Persistent bad breath can be a sign of digestive issues or other medical conditions like respiratory tract infections, chronic sinusitis or postnasal drip.
Information as per the ODA https://www.oda.ca/oral-health-basics/oral-conditions-diseases/bad-breath/
Braganza Periodontics - Peterborough Periodontist